A. Field of the Invention
This invention relates generally to the field of biological sample testing apparatus and systems, and more particularly to the subject of test sample cards which have one or more wells and fluid distribution channels formed therein for receiving a fluid or test sample containing a microbiological agent (such as a microorganism) and a reagent. The invention also relates to the subject of molds that are used to manufacture such devices.
B. Description of Related Art
A variety of test sample cards are described in the patent literature which have a well or reaction site for receiving a fluid sample containing a microbiological agent, such as a microorganism, and a reagent. The fluid sample is conveyed from a sample intake port to the well via fluid distribution channels formed in the surface of the card. Several representative patents include Meyer et al., U.S. Pat. No. 4,318,994, Charles et al., U.S. Pat. No. 4,116,775; Fadler et al., U.S. Pat. No. 4,038,151, Charles et al., U.S. Pat. No. 4,118,280, and O'Bear et al., U.S. Pat. No. 5,609,928, the contents of each of which are fully incorporated by reference herein. These patents describe a test sample card having a plurality of wells arranged in the test sample card body. The reagent is typically loaded in the wells of the card during the completion of manufacture of the card. The reagent typically comprises a growth medium for a microbiological agent in a fluid or test sample. It is known to load a different reagent in each of the wells of the card in order to perform identification testing of a fluid sample containing an unknown microbiological agent or organism. It is also known to use the cards to test the microbiological agent for susceptibility to antibiotics by loading various antibiotic reagents into the wells.
It is known in the art to apply a transparent adhesive membrane to at least the front and usually the rear opposite surfaces of the card in a manner so as to cover the wells and fluid distribution channels that connect a fluid intake port of the card to the wells. The transparent adhesive membrane prevents the reagent from being dislodged from the well during shipping and handling and serves as a liquid barrier to prevent the fluid sample introduced into the well from leaking around the edges of the well.
In the sample testing system described in the Charles et al '280 patent, after the well of the test sample card has been loaded with the fluid sample at the time of use, the card is incubated for a period of time to promote a reaction between the microorganism and the reagent, i.e., growth of the microorganism. The well is periodically subject to optical analysis by a transmittance light source and a detector which are positioned on opposite sides of the well, or by alternate detection methods. If the growth medium or reagent is specifically suited for or "matches up" with the particular microorganism in the fluid sample, the population of the microorganism increases substantially, or some other predetermined reaction, i.e., chemical reaction, takes place, which results in the well turning cloudy and thus having a change in light transmission characteristics. The detector determines the amount of light that is transmitted from the source through the well and the adhesive membranes covering the well. By comparing the transmittance measurements over a period of time, typically several hours at least, with an initial transmittance measurement, it is possible to determine whether in fact the reagent and microbiological agent are matched by virtue of the change in transmittance measurement reaching a threshold value, such as twenty five (25) or thirty (30) percent. The change in light transmission characteristics therefore can be used to indicate the presence of a specific microorganism in the well. Identification and susceptibility may also be detected by absorbency measurements where a fluorescent agent is provided in the growth medium.
Some microorganisms require a relatively long period of incubation time, such as up to 18 hours, in order for the reaction characteristics in the well to change sufficiently to produce a test result using transmittance analysis. Localized or partial detachment of the transparent adhesive membrane from the surface of the test sample card has been occasionally observed during such prolonged incubation. This in turn can cause two deleterious effects: (1) leaking of the fluid out of one well into another well resulting in cross-contamination between wells, and (2) the admission of air into the wells, interfering with the transmittance measurement. Both effects compromise the integrity of the microbiological sample testing process.
The present inventors have discovered that the problem of inadequate tape adhesion during incubation can be traced to the molding process by which the cards are formed during manufacture, and can be overcome by replacing prior art molding techniques with new molding techniques, described in detail herein. In order to appreciate this aspect of the invention, some background on molding of test sample cards may be useful to the general reader.
Basically, in the prior art the test sample cards are formed in a steel mold using conventional plastic molding techniques. Steel pins and positive surface features in the mold create the test sample wells, fluid channels, bubble traps, and other features in the test sample cards. It has been conventional in the prior art to polish the interior surface of the card mold by hand with a polishing tool in order to produce an extremely smooth mold surface. A smooth mold surface was generally necessary in order for the test sample card to be released from the mold.
Hand polishing of the mold in the space immediately adjacent to the pins and other features is particularly difficult, and essentially impossible to control with precision, since the human hand is virtually incapable of operating a polishing tool in exactly the same manner (e.g., with the same amount of pressure or for the same amount of time) over a relatively large and complex surface, such as a mold for a test sample card. For example, there may be inadequate room for the hand tool to polish immediately adjacent to the pins forming the test sample card in a uniform manner. One portion of the mold surface adjacent to the pin may be relatively easy to polish, but the portion opposite the pin may be very difficult to polish with the polishing tool. As another example, the operator of the tool may be unable to polish the mold evenly around the positive features forming the fluid distribution channels, due to space considerations, polishing tool size and shape constraints, and the operator's desire to avoid accidentally polishing (and therefore altering) the extremely fine positive fluid channel features in the mold.
The inventors have discovered that the result of the prior art hand polishing technique is that small surface contours (such as localized low spots and localized high spots) are unintentionally formed in the card in the vicinity of the wells and fluid distribution channels. These features are not generally visible to the naked eye, but are readily apparent under magnification. These surface imperfections negatively impact the adhesion of the transparent membrane to the test sample well by creating small gaps or spaces between the membrane and the card surface. These gaps can potentially become the site of localized separation of the membrane from the card surface in conditions of prolonged incubation sufficient to cause cross contamination between wells, the formation of air bubbles in the wells, or other intolerable conditions. Additionally, hand polishing the mold is an expensive, time consuming and difficult human process that is inherently unsuited for the requirements of test sample card molding technology.
In a primary aspect of the invention, the present inventors have invented a test sample card, mold and process for manufacturing the test sample card that substantially avoids these problems by providing features that promote a better adhesion of the transparent adhesive membrane to the test sample card than achieved in prior art test sample cards. Moreover, the invention completely avoids precision hand polishing of the mold in the parts of the card where surface contours are critical to tape adhesion.
Accordingly, an object of the invention is to provide a test sample card which has features promoting the improved adhesion of a transparent membrane to the card to thereby enable the card to be subject to incubation without detachment of the adhesive membrane from the surface of the card.
A further object of the invention is to provide a mold for manufacturing test sample cards which has a surface texture that provides a finish on the surface of the test sample card that has improved properties for adhering a membrane to the surface of the card.
Another object of the invention is to provide a mold for manufacturing a test sample cards that provides substantially flat, textured and uniform surfaces around the test sample wells and channel features, thereby promoting adhesion of the membrane to the surface of the card. A still further object of the invention is to provide improving molding techniques, including hot runner and valve gate techniques, in the process of molding the test sample card.
These and other objects, advantages and features of the invention will be more apparent from the following detailed description of a preferred and alternative embodiments of the invention.